adverb
up to this time; before now
preposition
before this time
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The heretofore undiscovered manuscript shed new light on the author's early work.
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We've never tried this method before, but heretofore, it seems to be working well.
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I never knew this spot existed, but heretofore, it's become my favorite hangout.
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The heretofore uncharted territory of my emotions was finally explored through therapy.